Freshwater Life in North-East Greenland. 335 



taking up some of the mud they are found buried in it. That they 

 can hibernate in the mud, as will be mentioned later, further wit- 

 nesses to their tenacity of life. 



In the middle of August we find that the females (even the 

 smaller) have eggs in the brood-pouch, as these shine through the 

 green chitinous shell as white points. ^ When the night-frost comes 

 towards the end of the month, many of the adult Apiis die (see 

 under Ostracoda); we then find them lying dead or dying on the 

 bottom of the lake; sometimes also they become frozen into the 

 thin ice and thus perish. Yet many living Apiis are still met with, 

 buried down in the mud or swimming about in the water. The 

 thin ice which forms definitely in the beginning of September, does 

 not trouble them very much to begin with; if they do not get 

 frozen into the bottom, we see them swimming up right to the 

 under surface of the ice and "walking" along this; or they remain 

 some time on the stalks of the herbage and the like; on these there 

 are often small bubbles of air and one can see the animals literally 

 imbibing these, as they are appreciably reduced or quite removed 

 after the animal has changed its position. As the ice gradually 

 becomes thicker and reaches the bottom, more and more Apus are 

 frozen into this and perish, unless they have buried themselves 

 down in the mud or migrated out into deeper water; if we take up 

 the dead animals, we find some among them which contain pale-red 

 eggs, the size of a pin's head, in their brood-pouch. These can 

 also be seen singly, deposited on the moss-plants and the like, and 

 the fact that they are enclosed in the ice does not seem to destroy 

 them. — 



When the ice on the banks thaws in the early summer (end of 

 May 1907 and beginning of June 1908), we find the dead Apus lying 

 by the banks, especially under stones; some of them contain the 

 above-mentioned eggs in the brood-pouch, and these eggs are also 

 found deposited on the water-plants. On keeping these eggs in a 

 glass I have observed, how they gradually assume a deeper, reddish 

 yellow colour, and little by little (after ca. one week) a small Apus 

 young, very like the adult, is formed inside. On the embryo it is 

 possible gradually to distinguish the frontal eye, carapace, body and 

 tail, and a week later after the ice of the lake had begun to melt 

 (middle of June 1907, end of June 1908), the characteristic fry of 

 the year are found, which as a kind of Metanauplius (the free- 

 swimming Nauplius is thus wanting in Apus glacialis) differs con- 

 siderably in size, form and colour from the adults. It is almost as 



' These are immature eggs; I have also found the females with the ripe eggs 

 at this time. 



XLV. 24 



